Avian ecological studies in a sagebrush community: bird responses to fire and territory dynamics in a sparrow population

• Main Author: Petersen, Kenneth Lee
• Format: Text
• Language: English
• Published: Iowa State University Digital Repository 1986
• Subjects: Animal ecology; Ecology and Evolutionary Biology; Environmental Sciences; Eremophila alpestris
• Online Access: https://lib.dr.iastate.edu/rtd/8289; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=9288&context=rtd

In 1980-1985, I documented the responses of nongame birds to a prescribed fire in an Idaho sagebrush (Artemisia spp.) community, and I tested the hypothesis that territory shifts by sage sparrows (Amphispiza belli) represented adaptive adjustments in site use. The burn was incomplete (45%) but altered major components of the vegetation. Burned plots supported 1 more bird species than controls, and although total bird densities declined the year after fire, they were greater on burned plots than on controls by the fourth postburn year. Sage sparrow numbers were unaffected by fire; Brewer's sparrow (Spizella breweri) numbers declined in the 2 breeding seasons immediately after fire but increased dramatically thereafter. Sage thrashers (Oreoscoptes montanus) showed no response to fire; horned larks (Eremophila alpestris) and vesper sparrows (Pooecetes gramineus) colonized burned areas. Return rate of male sage sparrows was somewhat reduced 2 years after fire, nest survival probability was greater on burned plots than on controls the first year after fire, and nestling growth rate increased the first year postburn. Sage sparrow mating success, clutch size, and fledgling production were not influenced by fire. Brewer's sparrow return rate, mating success, clutch size, nest survival probability, fledgling production, and nestling growth were unaffected by fire. Burning altered nest-site characteristics of both sparrows;I predicted that territory shifts by sage sparrows should (1) result in changes in territory characteristics, (2) be influenced by previous reproductive success and result in greater success, and (3) decline in magnitude for individual males over time. Habitat features of territories changed little as a result of shifts, and were unrelated to reproductive success. Territory size increased after shifts, and was positively related to reproductive success. The magnitude of territory shifts was negatively correlated with preshift fledgling success, and after shifts, males experienced greater reproductive success than before. Successive territory shifts by individual males became progressively smaller. Thus, territory shifting by sage sparrows seems to be adaptive behavior aimed primarily at increasing territory size.